This invention relates to viscoelastic fluids which contain a surfactant and to methods of suspending particles using such viscoelastic fluids.
It is known to thicken the aqueous phase of a suspension of solid particles or emulsified droplets. The addition of thickeners increases the viscosity of the aqueous phase and thereby retards settling of the particles or droplets. Such retardation is useful to maintain the particles or droplets in suspension during the storage, use, and/or transport of the suspension.
Polymeric thickeners, e.g. starches, which thicken by entanglement of the polymeric chains, have been used to viscosify the aqueous phase of suspensions. Such thickeners can degrade under the influence of mechanical shear or chemical scission (e.g. by oxidation or hydrolysis) of the polymeric chains which results in a loss of viscosity and, thus, suspension stability.
Cationic surfactants have been found which form rodlike micelles under certain conditions. The presence of the rod-like micelles imparts to the fluid viscoelastic properties. However, cationic surfactants tend to have high toxicity and very low biodegradability.
The present invention provides a viscoelastic fluid useful as a thickener for the suspension of particles. The viscoelastic fluids consist of an amphoteric/zwitterionic surfactant and an organic acid/salt and/or inorganic salts.
Thus, this invention specifically relates to a viscoelastic fluid comprising:
(1) an aqueous medium;
(2) an amount of a surfactant selected from the group consisting of amphoteric surfactants, zwitterionic surfactants and mixtures thereof, effective to render said aqueous medium viscoelastic; and
(3) a member selected from the group consisting of organic acids, organic acid salts, inorganic salts, and combinations of one or more organic acids or organic acid salts with one or more inorganic salts.
In yet another embodiment of the present invention, the invention relates to a viscoelastic fluid consisting essentially of:
(1) an aqueous medium;
(2) an amount of a surfactant comprising an amine oxide surfactant; and
(3) an anionic surfactant containing a hydrophobe having at least 14 carbon atoms.
The term xe2x80x9cviscoelasticxe2x80x9d refers to those viscous fluids having elastic properties, i.e., the liquid at least partially returns to its original form when an applied stress is released. The thickened aqueous viscoelastic fluids are useful as water-based hydraulic fluids in lubricant and hydraulic fracturing fluids to increase permeability in oil production.
The present invention also relates to a method for distributing suspended solid particles such as excavation by-products in a fluid comprised of the viscoelastic fluid of this invention, wherein the solid particles remain suspended for an extended period of time to a side, by transporting the fluid to a site while the solid particles remain suspended in the fluid and depositing the fluid to such site.
This invention also relates to a method for fracturing a subterranean formation comprising pumping the inventive viscoelastic fluid through a wellbore and into a subterranean formation at a pressure sufficient to fracture the formation.
This invention also relates to a detergent formulation comprising a detersive surfactant in admixture with a viscoelastic fluid of this invention.
This invention also relates to the use of the viscoelastic fluid as a drift control agent for agricultural formulations. In this regard, this invention relates to an aqueous formulation of an agricultural chemical and an amount of the viscoelastic fluid of this invention sufficient to increase the average droplet size of a spray of said formulation.